Unitized fuel cell electrode gasket assembly

ABSTRACT

A foam gasket ( 35 ) is adhered to an anode substrate ( 14 ) by sealant material, such as a thermoplastic polymer, a thermoset polymer or an elastomeric polymer, which is impregnated ( 31 ) to provide an edge seal to the anode substrate. In one embodiment, a foam gasket ( 36 ) is adhered to the cathode substrate ( 26 ) by the sealant material which is impregnated ( 32 ) to provide a gas edge seal to the cathode substrate. Each fuel cell is completed during the formation of a fuel cell stack by compressing the fuel flow field plates and oxidant flow field plates to the unitized electrode assembly with gaskets. In a second embodiment, the oxidant flow field plate ( 27 ) is adhered to the cathode substrate by the sealant material which is impregnated into the cathode substrate to provide a gas edge seal, and the fuel flow field plate ( 18 ) is adhered to the oxidant flow field plate ( 27 ) by means of the sealant material ( 53 ). The entire fuel cell with gasket ( 9   a ) is formed in a single hot lamination step ( 45   b ).

TECHNICAL FIELD

[0001] This invention relates to a proton exchange membrane (PEM) fuelcell in which the edge seals of the cathode and/or anode diffusionlayers are joined to a gasket by means of the substrate-sealingthermoplastic film.

BACKGROUND ART

[0002] As is known, a PEM fuel cell has catalyst layers on the cathodeand anode side of the membrane, possibly with optional diffusion layersformed as a coating on the cathode and anode substrates, respectively,which are on the non-membrane sides of the cathode and anode catalysts.The substrates, also known as carbon papers, are highly porous, whichmay, for instance, have on the order of 70% porosity with pores on theorder of 30 microns in diameter. In order to prevent the oxidantreactant gas (such as air) and the fuel reactant gas (such as a hydrogencontaining gas) from escaping through the side edges (those edges not incommunication with respective external manifolds) it has been known toprovide edge seals to the anode and cathode substrates.

[0003] In FIG. 1, an exemplary PEM fuel cell 9, of the general typeknown to the prior art, includes a proton exchange membrane 11, an anodecatalyst 12 which may comprise a coating on the membrane of on the orderof 10 micron thickness, an anode substrate 14, which may, optionally,have an anode diffusion layer comprising a coating 15 on the order of 25microns on the surface of the substrate 14. The fuel flow field maytypically comprise an anode flow field water transport plate 18 havingfuel reactant gas flow channels 19 therein and a degree of porosity topermit water, typically from a coolant flow channel (not shown), to beabsorbed in the fuel reactant gas so as to provide moisture through theanode layers to the membrane 11. Similarly, on the cathode side, thereis a cathode catalyst 22, there may be an optional cathode diffusionlayer 23, a cathode substrate 26, and an oxidant reactant gas flowfield, typically comprised of a cathode flow field water transport plate27 having oxidant reactant gas flow field channels 28 therein. In FIG.1, external fuel reactant gas manifolds (not shown) will be in fluidcommunication with the fuel reactant gas flow field channels 19, andexternal oxidant reactant gas manifolds (not shown) will be in fluidcommunication with the oxidant reactant gas flow field channels 28.

[0004] To prevent gases from leaking from the substrate layers 14, 26,it is common to employ an edge seal 31, 32 which consists of athermoplastic film such as polyvinylidene chloride (KYNAR®), or anelastomer, such as a silicone rubber, extruded into the substrate.Plastic films 33 may be provided as fillers at the edges of the anodeand cathode catalysts and optional diffusion layers.

[0005] Interfacial seals between the anode water transport plate 18 andthe anode substrate 14, as well as between the cathode water transportplate 27 and the cathode substrate 26 may typically comprise siliconerubber closed cell foam gaskets 35, 36, respectively, held in place,prior to compression in making the fuel cell stack, by pressuresensitive adhesive 37, 38. The pressure sensitive adhesive may be anacrylic adhesive or a silicone adhesive. It has been found that if anacrylic adhesive is used, the life of the fuel cell is limited tobetween 2,000 hours and 5,000 hours because of gas leakage due to thecorrosion of the adhesive. A problem with either adhesive is the extrasteps required to produce a unitized electrode assembly 40 (includingthe catalyst coated membrane and the substrates (with or withoutdiffusion layers), and the extra steps required to produce the flowfield seals assembly.

[0006] As illustrated in FIG. 2, the prior art process requires a hotlamination step 43 to provide the anode substrate 14 with theimpregnated seal 31. A similar hot lamination step 44 is required toprovide the cathode substrate 26 with the impregnated seal 32. Then, athird hot lamination step 45 is required to join the substrates 14, 26with the catalyst coated membrane 11, 12, 22, in order to produce theunitized electrode assembly 40. The flow field plates 18, 27 have theirrespective foam gaskets 35, 36 adhered to them by pressure sensitiveadhesive 37, 38 in compression steps 46, 47 to provide fuel and oxidantflow field plates with seals 48, 49. These are then brought together,along with other, similar fuel cell components to form a fuel cell stackassembly 50.

[0007] Fuel cells of the type described with respect to FIG. 1 areillustrated in U.S. Pat. Nos. 6,020,083, 6,159,628, and 6,187,466.

DISCLOSURE OF INVENTION

[0008] Objects of the invention include: an improved PEM fuel cellsubstrate gas edge seal; a PEM fuel cell substrate gas edge seal whichcan be provided on a high speed production basis; a low cost andeffective PEM fuel cell substrate gas edge seal; reducing the number ofprocessing steps required to produce a PEM fuel cell; and a PEM fuelcell that will operate in excess of 10,000 hours without gas leakage.

[0009] According to the present invention, the thermoplastic filmimpregnated into the anode substrate and the cathode substrate so as toform respective gas edge seals is utilized in providing a gas edge sealbetween at least one substrate and a corresponding reactant gas flowfield plate, which may comprise a water transport plate in someembodiments. In a first embodiment of the invention, the edge sealimpregnated thermoplastic is used as the bond between each substrate anda corresponding closed cell foam gasket, the gasket sealing the jointbetween the respective reactant gas flow field plate and correspondingsubstrate when the fuel cell parts are compressed together in theprocess of forming a fuel cell stack. According to another embodiment ofthe invention, at least one reactant gas flow field plate is bondeddirectly to a corresponding substrate by means of the impregnated edgeseal thermoplastic of the corresponding substrate. The invention notonly provides adhesion which will last well in excess of 10,000 hours ofoperation, but it also reduces the number of steps required to form afuel cell, and to form a fuel cell stack.

[0010] Other objects, features and advantages of the present inventionwill become more apparent in the light of the following detaileddescription of exemplary embodiments thereof, as illustrated in theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a simplified, partial, sectioned perspective view of aprior art PEM fuel cell.

[0012]FIG. 2 is a simplified diagram illustrating the process ofproducing the fuel cell of FIG. 1.

[0013]FIG. 3 is a side elevation view of a portion of a fuel cell inaccordance with a first aspect of the invention.

[0014]FIG. 4 is a chart illustrating the process of producing a fuelcell incorporating the invention illustrated in FIG. 3.

[0015]FIG. 5 is a fractional perspective view of a portion of a fuelcell illustrating a second aspect of the present invention.

[0016]FIG. 6 is a chart illustrating the process of producing a fuelcell incorporating the invention of FIG. 5.

MODE(S) FOR CARRYING OUT THE INVENTION

[0017]FIG. 3 illustrates one aspect of the present invention. Therein,the silicone rubber closed cell foam gasket 35 or 36 is adhered directlyto a related one of the substrates 14 or 26, respectively, by therelated sealant material 31 or 32 during the hot lamination which causesthe substrate 14 or 26 to become impregnated with the plastic. Thesealant material may be a thermoplastic polymer, a thermoset polymer, oran elastomeric polymer. The sealant material may be a film, a coating,an extrusion or any form that is conducive to high speed manufacturing.This process is illustrated in FIG. 4, in which a single hot laminationprocess 45 a not only impregnates the anode substrate 14 and the cathodesubstrate 14, but it joins those substrates together with the foamgaskets 35 or 36 and the catalyst coated membrane 11, 12, 22. This formsa unitized electrode assembly with gaskets 51, which only need becombined with the fuel flow field plate 18 and the oxidant flow fieldplate 27 together with other similar fuel cell components to form thefuel cell stack assembly 43. Thus, instead of the three hot laminationsteps 43, 44, 45 in the prior art process illustrated in FIG. 2, onlyone hot lamination step 45 a is required in accordance with this aspectof the present invention.

[0018] A further aspect of the invention is illustrated in FIG. 5.Therein, the gasket 35 is adhered by means of the thermoplastic 31 tothe anode substrate 14, as described with respect to FIG. 3. But, thecathode substrate 26 is not provided with a gasket. Instead, the oxidantflow field plate 27 is adhered directly to the cathode substrate 26 bymeans of the thermoplastic material 32 at the time that thethermoplastic material 32 is impregnated into the cathode substrate 26.The fuel flow field plate 18 is joined by a thermoplastic material 53 tothe oxidant flow field plate 27, thus eliminating one gasket andeliminating the need to shape the oxidant flow field plate with a notchto accommodate a gasket, as is illustrated in FIG. 3. Thus, an integralfuel cell is formed when this aspect of the invention is employed. Thefuel call can be unitized with a single hot lamination process 45 b, asillustrated in FIG. 6, which provides a fuel cell with gasket 9 a. Insuch a case, only assembly is required to bring all of the fuel cellstogether in a fuel cell stack 43, in which the foam gasket 35 of onefuel cell will mate into the notch of a fuel flow field plate 18 of anadjacent fuel cell. The invention may, instead, adhere the fuel reactantflow field 18 to the anode substrate 14 and provide gaskets 36 on thecathode substrate 27. Of course, accommodations for the end cells willbe made, which is well within the skill of the art in the light of theteachings herein.

[0019] Although the invention has been described relative to a fuel cellusing external reactant manifolds (not shown), the invention may beapplied to fuel cells containing internal reactant manifolds. Theinvention may be incorporated into fuel cells in which the flow fieldsmay either be porous or solid flow fields known in the art.

[0020] The aforementioned patents are incorporated herein by reference.

[0021] Thus, although the invention has been shown and described withrespect to exemplary embodiments thereof, it should be understood bythose skilled in the art that the foregoing and various other changes,omissions and additions may be made therein and thereto, withoutdeparting from the spirit and scope of the invention.

I claim:
 1. A fuel cell comprising: a catalyst coated proton exchangemembrane disposed between an anode substrate and a cathode substrate,each of said substrates being provided with an edge seal formed of asealant material extruded into the substrate by a hot laminationprocess, at least one of said substrates having a foam gasket adheredthereto by said sealant material film during said hot laminationprocess.
 2. A fuel according to claim 1 wherein both of said substrateshave a foam gasket adhered thereto by said sealant material during saidhot lamination process.
 3. A fuel cell according to claim 1 wherein:said sealant material comprises a thermoplastic polymer.
 4. A fuel cellaccording to claim 1 wherein: said sealant material comprises athermoset polymer.
 5. A fuel cell according to claim 1 wherein: saidsealant material comprises an elastomeric polymer.
 6. A fuel cellaccording to claim 1 wherein only one of said substrates has a foamgasket adhered thereto, and wherein: the other of said substrates has areactant gas flow field plate adhered thereto by said sealant materialwhich is extruded into said substrate by said hot lamination process,and a reactant gas flow field plate related to said one substrate isadhered to said first reactant gas flow field plate by said sealantmaterial during said hot lamination process, to form an integral fuelcell with a gasket.
 7. A fuel cell stack comprising a plurality of fuelcells according to claim 6 compressed together, whereby the foam gasketof one fuel cell provides a gas seal with the second reactant flow fieldplate of a fuel cell adjacent thereto in said stack.